1. Mobile IP-2 CS441 – Mobile & Wireless Computing
Department of Computer Science
Southern Illinois University Carbondale
CS441 – Mobile & Wireless Computing
Mobile IP-2
Dr. Kemal Akkaya
Some slides are adapted from:
Dr. Ibrahim Korpeoglu, Bilkent University
Mobile & Wireless Computing

2. Mobile Agent Discovery
How a mobile node discovers the home and foreign agents when it travels?
Agents periodically broadcast their presence (advertisement) on a link ( a wireless link – , or a wired link – Ethernet)
These broadcasts are agent advertisement messages.
An agent advertisement message is an ICMP router advertisement message with special extension.
The special extension is called Mobility Agent Extension.
A mobile node receiving the advertisement understand from the IP addresses included in the advertisement:
Whether it is in the home network or not?
Whether it has moved to new location or not.
This understanding is at the IP level
A mobile already knows that it has moved at the physical link level if has moved.
Mobile & Wireless Computing

3. Data Transfer to the Mobile Node in Mobile IPHA 2 MN
Internet
home network 3
receiver FA
foreign
network
1. Sender sends to the IP address of MN,
HA intercepts packet
2. HA tunnels packet to COA, here FA,
by encapsulation
3. FA forwards the packet to the MN 1 CN
sender
Mobile & Wireless Computing

4. Agent Advertisement Message
Ver HL
TOS
Total Length
Identification
Flags
Fragm. Offset
TCP/IP Protocol Stack
in a Host
TTL
Protocol
Header Checksum
IP Header
Src Address
Applications
Dest Address
Type
Code
Checksum
ICMP Router Advertisement Message
TCP
UDP
NAddr=0
Addr Size
Lifetime
Type
Length
Sequence Number
ICMP
IGMP
Mobility Agent Extension IP
Lifetime
Flags
Reserved
Zero or more care-of-addresses
……….
ARP
RARP
Link
Layer
FLAGS
R: Registration requires (with the foreign agent)
B: Foreign agent is busy
H: The agent is home agent.
F: The agent is foreign agent
M: Minimum encapsulation
G: GRE encapsulation
V: Van Jacobson Header Compression
Mobile & Wireless Computing

5. Registration
After a mobile detects at the IP (ICMP) layer that it has moved to a new location, it starts registration procedure with the home agent.
The aim of the registration is to let the home agent know mobile’s current care-of-address. Mobile obtains this care-of-address either from the foreign agent or from a server like DHCP server.
Registration procedure consists of sending a Registration Request Message from mobile to home agent and a Registration Reply Message from home agent to mobile
Registration messages has to go through Foreign agent.
Foreign Agent just forwards these registration messages back and forth
Foreign agent is a passive entity in registration.
Registration messages sent over UDP to port number 434.
Mobile & Wireless Computing

6. Registration Request Mobile & Wireless Computing 6 0 8 16 31 HA REQ FA HA
REQ FA
Type
Flags
Lifetime
REQ
Home address
Type: Type of the Mobile IP Message:
1 – Registration Request.
Lifetime: Number of seconds registration is valid.
Home address: The home IP address of the mobile
Home agent: The IP address of the home agent. Care-of-address: The current IP address of the mobile –
this is then end of the tunnel.
Identification: Used for replay protection.
Extensions: Security extensions can be added to protect
from malicious people.
Flags:
S: Simultaneous binding. B: Broadcast – Home agent will tunnel broadcast datagrams to the mobile
D: Mobile node is using a collocated care-of-address – that means there is no foreign agent and mobile node will decapsulate the packets itself.
M: Mobile node requests the home agent to encapsulate the packets using Minimal Encapsulation
G: Mobile node requests the home agent to encapsulate the packets using GRE Encapsulation MN
Home agent
Care-of--address
Identification
Extensions
…..
Registration Request Format
IP Header
UDP Header
Mobile IP Message
Extensions
Mobile & Wireless Computing

7. Registration Reply Mobile & Wireless Computing 7 RPL HA FA RPL MN
Type
Code
Lifetime
Home address
Home agent
Type: 3 – Registration Reply
Code: Indicates the result of registration Some code values:
0 registration accepted
66 insufficient resources at foreign agent
70 poorly formed request
130 insufficient resources at home agent
131 mobile node failed authentication
Lifetime: The granted life time by home agent for
registration
Identification
Extensions
…..
Registration Reply Format
Mobile & Wireless Computing

8. Care-of-Address Types
Normal Care-of-address
The care-of-address that mobile obtains at a new location is the IP address of a foreign agent serving at that new location.
Registration and communication has to go through foreign agent
Co-located care-of-address
There is no separate foreign agent present at the new location
Mobile obtains an IP at the new location through some standard mechanisms like DHCP.
This IP address is called collocated IP address.
The foreign agent functionality is executed at the mobile node itself.
The mobile node decapsulates the tunneled packets coming from home agent.
Registration and communication is done directly between mobile and home agent.
Mobile & Wireless Computing

9. Routing and Tunneling
When a correspondent host sends an IP packet to a mobile (to its home address), packet is routed first to home agent of mobile through normal routing.
Home agent intercepts the packet and encapsulates it and tunnels it to the care-of-address (tunnel exit point) of the mobile.
The encapsulated packet is delivered to the care-of-address using normal routing.
There are various encapsulation methods:
IP-IP Encapsulation
Minimal Encapsulation
GRE (Generic Routing Encapsulation) Encapsulation. C
Tunnel HA FA M
Encapsulated IP Packet
Mobile & Wireless Computing

10. IP-IP Encapsulation at Home Agent
Ver HL
TOS
Total Length
Home agent encapsulated the IP
packet inside another IP header and
sends it to the care-of-address of
mobile.
Identification
Flags
Fragm. Offset
Outer
Header
TTL
Protocol=4
Header Checksum
Src Address = Home agent addres
Dest Address = Care-of-Address of M
Ver HL
TOS
Total Length
Identification
Flags
Fragm. Offset
Inner
Header
TTL
Protocol
Header Checksum
Src Address = Addr of C
An IP packet is received at the
home agent from a correspondent
host for a mobile host.
Dest Address = Addr of M
IP PAYLOAD
Mobile & Wireless Computing

11. IP-IP Decapsulation at the Care-of-Address
Ver HL
TOS
Total Length
An encapsulated IP packet is received
at the foreign agent (or at the mobile
itself for a collocated care-of-address).
Receiver understands that the packet
is IP-IP encapsulated by looking
at the protocol field (which is 4).
Identification
Flags
Fragm. Offset
Outer
Header
TTL
Protocol=4
Header Checksum
Src Address = Home agent addres
Dest Address = Care-of-Address of M
Ver HL
TOS
Total Length
Identification
Flags
Fragm. Offset
Inner
Header
TTL
Protocol
Header Checksum
Src Address = Addr of C
Dest Address = Addr of M
Receiver forwards (not routes)
the decapsulated IP packet to the mobile node using
link-level mechanisms!
IP PAYLOAD
Mobile & Wireless Computing

12. Decapsulation again Mobile & Wireless Computing 12 Mobile Node
Foreign Agent
APPS
APPS
Home
Agent
TCP/UDP
TCP/UDP
dst src dst src
ds t src
IP_M
IP_C
IP_F
IP_H
IP_M
IP_C
IP_H
IP_F
IP_M
TUNNEL
MAC_F
IP_M
IP_C
MAC_F
MAC_M
MAC_M
Mobile & Wireless Computing

13. Minimal Encapsulation at Home Agent
Tunneled to
care-of-address
Ver HL
TOS
Total Length
Identification
Flags
Fragm. Offset
Outer
header
TTL
Proto=55
Header Checksum
Ver HL
TOS
Total Length
Src Address = Addr of home agent
Identification
Flags
Fragm. Offset
Dest Address = Care-of-addr of mobile
TTL
Protocol
Header Checksum
Protocol S
Reserved
Header Checksum
Src Address = Addr of C
Minimal
Inner header
Src Address = Addr of C
Dest Address = Addr of M
Dest Address = Addr of M
IP PAYLOAD
IP PAYLOAD
Encapsulated using
Minimal Encapsulation
Method
Packet comes from
Correspondent host
Mobile & Wireless Computing

14. Sending packets between mobile and foreign agent
When a mobile moves to a new location, a foreign should be broadcasting (IP and link layer broadcast) advertisements on the link (sub-network).
Mobile will be able to receive this broadcast message and will learn:
The IP address of the foreign agent (this will be the care-of-address of the mobile most of the time).
The hardware (MAC or link-level address) of the foreign agent.
When mobile sends a registration packet through this foreign agent, the foreign agent will learn:
The home address of the mobile
The hardware (MAC or link level) address of the mobile.
The registration packet will be sent directly to the foreign agent by using the MAC address of the foreign agent (No need to do ARP request).
Mobile & Wireless Computing

15. Broadcasted Mobile Agent Advertisement
Mobile Node - M
Foreign
Agent - FA
Mobile Node receives
broadcast frame and
learns the MAC and IP
address of the FA. It
stored this info.
Broadcasted Mobile Agent Advertisement
FA periodically broadcasts advertisements.
MAC broadcast address is used. No need for ARP.
Mobile Node sends
a registration request
message directly to FA.
It is not using ARP protocol to obtain the MAC address of FA.
FA learns the MAC address of a mobile from the registration request message. Learns also the home address of the mobile. This info is stored.
Registration Request
Registration Reply
Reply is sent directly to the MAC address of mobile. No need for ARP.
DATA
Mobile node sends data
Directly to the MAC address
of FA. No ARP needed.
FA sends data
directly to the MAC address of FA. No ARP needed.
DATA
Mobile & Wireless Computing

16. Sending Data from Foreign Agent to Mobile
Node
Foreign Agent
APPS
Other
Fields
UDP
TCP/UDP
Dst
Src
IP Payload
IP_M
IP_C ….
IP_F
IP_M
MAC_F
IP Payload
IP_M
IP_C ….
type
MAC_F
MAC_M
MAC_M
Src
(6 b ytes)
Dst
(6 bytes)
IP Header
Ethernet Header
(link level header)
Mobile & Wireless Computing

17. Sending Data from Mobile to Foreign Agent
Node
Foreign Agent
APPS
APPS
Other
Fields
IP Payload
TCP/UDP
TCP/UDP
Src
Dst ….
IP_M
IP_C
IP Payload
IP_F
IP_M
MAC_F
MAC_M
type ….
IP_M
IP_C
IP Payload
MAC_F
MAC_M
Dst
(6 bytes)
Src
(6 b ytes)
IP Header
Ethernet Header
(link level header)
Mobile & Wireless Computing

18. How to attract packets at the Home network
Physical Home Network
Proxy ARPing enabled
MAC_R
IP_M
MAC_H
Internetwork
Router
Proxy ARP table
Home Agent
IP Payload
IP_M
IP_C ….
MAC_H
An IP Packet
came from a
correspondent host
destined to a Mobile Host
Broadcast ARP Request
Who has IP_M
Unicast ARP Reply
I have IP_M, My MAC addr=MAC_H
IP Packet put into a Ethernet Frame
IP Payload
IP_M
IP_C
type
MAC_R
MAC_H
Mobile & Wireless Computing

19. Proxy ARPing
The packet comes to the last router that the home subnetwork is connected to.
The router will try ro resolve the IP address of Mobile (IP_M) into the corresponding MAC layer address (Hardware address).
For this pupose, it will broadcast an ARP request packet
Since the mobile is not at home subnet, it will not be able to answer ARP request.
Home agent will answer instead of the Mobile node. In order to do this, home agent should be configured to do proxy ARPing.
Home agent replies to the ARP request with an ARP reply, including its MAC address (MAC_H) as the MAC level address corresponding to the IP address of the Mobile.
The router, upon receiving the ARP reply, will send the IP packet to the MAC address of the home agent.
In this way, the home agent attracts the IP packets that are destined to the mobile node.
Mobile & Wireless Computing

20. Example: Gratuitous ARP
Correspondent
Host
(IP_C)
(IP_X, MAC_X)
(IP_H, MAC_H)
Host X
IP_M  MAC_M
Home Agent
IP_M  MAC_H
INTERNET
Home Subnet
Router
REGISTRATION
(IP_R, MAC_R)
IP_M  MAC_M
(IP_M, MAC_M)
IP_M  MAC_H
Broadcast Gratuitous ARP Request
(IP_M, MAC_M)
IP_M
.....
IP_M
MAC_H 1
Prot
type Hw
type
MAC_H
FFFFFF
Target IP
Target
MAC
Sender
MAC
Sender IP
Home Agent Broadcast an Gratuitous ARP Request on the LAN.
Any receiveing host will update its ARP cache.
Mobile & Wireless Computing

21. Problems with Mobile IP
Problem 1 : Triangular Routing
CN sends all packets via HA to MN
Higher latency and network load
“Solution” – comes with Mobile IPv6
CN learns the current location of MN
Direct tunneling to this location
HA or MN informs a CN about the location of MN
Problem of the solution
Cache consistency problems!
MN moves to a new network (handoff) See next slide
Security problems!
COA is provided
Mobile & Wireless Computing

22. Problems with Mobile IP
Problem 2 : Change of FA (COA) or Handoff
Packets on-the-fly during the change can be lost
“Solution”
New FA informs old FA to avoid packet loss, old FA buffers and then forwards remaining packets to new FA
This information also enables the old FA to release resources for MN
Solutions to Problems : Mobile IPv6 – Comes with IPv6
Mobile IPv6 comes with stronger security
Thus, route optimization is a default!!
No need for FOA
MN takes care of everything
No Triangular Routing
Mobile & Wireless Computing